1. Field of the Invention
The present invention relates to a reception apparatus used in a digital communication.
2. Description of the Related Art
Conventionally, in a reception apparatus used in a digital communication (hereinafter referred to as “digital reception apparatus”), on the assumption that the linearity is maintained in the reception processing on received signals, the demodulation processing has been executed on the received signals subjected to the reception processing. When the linearity is not maintained in the reception processing on received signals, characteristics of demodulated signals deteriorate which are obtained by performing the demodulation processing on the reception-processing processed received signals.
For example, a case is assumed that in the demodulation processing on the reception-processing processed received signals, unnecessary frequency signal components are divided from the reception-processing processed received signals to obtain only necessary frequency signal components. In this case, when the linearity is not maintained in the reception processing on received signals, it is difficult to divide the unnecessary frequency signal components from the reception-processing processed received signals, and also, even necessary frequency signal components are sometimes removed from the reception-processing processed received signals. The characteristics of the demodulated signals obtained by the demodulation processing thereby deteriorate.
Accordingly, the conventional digital reception apparatus is designed to highly maintain the linearity in the reception processing to the received signals.
Meanwhile, recent digital communications require communications for fast transmitting a large amount of information. In order to satisfy such a requirement, the quadrature amplitude modulation (QAM) or the like is applied as a modulation scheme, and/or the spread spectrum system in which a plurality of channels are multiplexed in a communication band and/or the OFDM (Orthogonal Frequency Division Multiplexing) system is used as a communication system.
However, when QAM or the like is applied as a modulation scheme, and/or the spread spectrum system and/or the OFDM system is used as a communication system, a signal amount per communication band is increased. Therefore, the power/amplitude of received signals is increased, which causes a problem that it becomes very difficult to maintain the linearity in the reception processing to the received signals. As a result, the characteristics of the demodulated signals obtained by the demodulation processing deteriorate.
Therefore, in the recent case where the communication system is applied that increases the signal amount per communication band, a technique has been quite desired that highly maintains the linearity in the reception processing in the digital reception apparatus.